This invention relates to a flow control device used for controlling the rate of flow of liquid passing through a liquid supply tube of a liquid transfer set, such as a solution administration set.
FIGS. 1 to 3 show a prior art liquid flow device of this type. As is shown, the device comprises a housing 1 with a liquid supply tube insertion channel 2. Opposite side walls of the liquid supply tube insertion channel 2 are formed with bearing grooves 4 (FIGS. 2 and 3). A manually movable roller 3 has its shaft 3b mounted in the bearing grooves 4 such that it is movable along the liquid supply tube insertion channel 2. The liquid supply tube insertion channel 2 has a bottom surface 2a which is inclined by a predetermined (FIG. 3) angle with respect to the bearing grooves 4. A liquid supply tube 5 is passed through the bottom surface 2a and periphery 3a of the roller 3. The roller 3 is manually moved to be closer to or remoter from the bottom surface 2a of the liquid supply tube insertion channel 2 to vary the extent of squeezing of the liquid supply tube 5 so as to control the rate of flow of liquid.
In the above prior art flow control device, the liquid supply tube 5 is made of a soft thermoplastic polymer such as polyvinyl chloride and is therefore subject to a phenomenon of creep. Squeezed opposite edges of the liquid supply tube initially have strong restoring force and tend to restore to the initial state. In long use, however, the restoring force becomes weaker, so that the initially formed inner flow passage of the liquid supply tube 5 is changed in long use. This means that it is difficult to obtain a stable rate of flow.
In a different aspect, with the prior art flow control device it is necessary to provide a wide range of rate of flow, from zero to a very high rate. Also, a certain limitation is imposed on the length of the housing 1 by considerations of the durability and operability. Therefore, it is difficult to reduce the inclination of the bottom surface 2a of the liquid supply tube insertion channel 2. This means that it is difficult to obtain flow control, particularly fine flow control.
Other prior art pertaining to the flow control device according to the present invention includes Japanese Patent Disclosures 47-1540, 50-41374, 52-81718, 52-108691, 52-142331, 53-103685, 53-144191, 53-148193, 54-2515, 54-10426, 54-10427, 54-60792, 54-108492, 55-72986, 58-30593, 61-41462, 50-125591, 50-125592 and 51-102392, Japanese Utility Model Disclosures 53-18089, 53-42499, 54-3096, 54-66697, 54-72398, 54-183196, 55-2338, 57-12868, 57-188976, 57-194958, 57-194959, 58-58150, 58-58151, 59-5939, 59-88563, 5992265, 61-151742, 61-156935, 61-180042, 61-180043 and 54-131395, Japanese Patent Publications 48-36526, 55-27986, 55-27987, 55-31351, 57-8342, 60-27870, 55-8573, 56-43578, 56-49013, 58-22224 and 58-44384, Japanese Utility Model Publications 51-45911 and 59-9642 and Japanese Patent Announcement 56-501619.